1. Field of the Invention
The present invention relates to a sensor-incorporated wheel support bearing assembly having a load sensor for detecting a load acting on a bearing portion of a wheel.
2. Description of the Prior Art
For safety travel of an automotive vehicle, the wheel support bearing assembly equipped with a sensor for detecting the rotational speed of one of automotive wheels has hitherto been well known in the art. While the automotive traveling safety precaution is hitherto generally taken by detecting the rotational speed of a wheel of various parts, but it is not sufficient with the detection of only the rotational speed of the wheel and, therefore, it is required to achieve a safety control of the automotive vehicle with the use of other sensor signals.
In view of this, it may be contemplated to achieve a posture control based on a load acting on each of wheels during travel of an automotive vehicle. By way of example, a large load acts on the outside wheels during the cornering, on the wheels on one side during the run along left and right inclined road surfaces or on the front wheels during the breaking and, thus, a varying load acts on the vehicle wheels. Also, in the case of the uneven live load, the loads acting on those wheels tend to become uneven. For this reason, if the loads acting on the wheels can be detected as needed, suspension systems for the vehicle wheels can be controlled beforehand based on results of detection of the loads so that the posture of the automotive vehicle during the traveling thereof (for example, prevention of a rolling motion during the cornering, prevention of downward settling of the front wheels during the breaking, and prevention of downward settling of the vehicle wheels brought about by the uneven distribution of live loads) can be controlled. However, no space for installation of the load sensor for detecting the load acting on the respective vehicle wheel is available and, therefore, the posture control through the detection of the load can hardly be realized.
Also, in the event that in the near future the steer-by-wire is introduced to provide the system, in which the wheel axle and the steering come not to be coupled mechanically with each other, and such system is increasingly used, information on the road surface comes to be required to transmit to the steering wheel held by a driver by detecting a load acting in a direction of the wheel axis.
In order to meet those needs, the wheel support bearing assembly has been suggested, in which a strain gauge is affixed to an outer race of the wheel support bearing assembly so that the strain gauge can detect a strain acting on the outer race (See, for example, the Japanese Laid-open Patent Publication No. 2003-530565, published Oct. 14, 2003).
However, since the outer race of the wheel support bearing assembly has at least one raceway defined therein and therefore must have a sufficient strength and also since it is manufactured through complicated process steps including metal forming, turning, heat treatment and grinding, the affixing of the strain gauge to the outer race is not efficient in productivity and is costly when it comes to mass production thereof. It is difficult to detect a strain on the outer race with good sensitivity.
In order to improve productivity, attempts have been made to fit a ring member to the peripheral surface of the outer race and to affix the strain gauge to the ring member. However, the detection of a strain on the outer race with good sensitivity has not been yet achieved.